Theoretical model of 180° domain-wall structures and their transformation in ferroelectric perovskites

Two kinds of 180^∘{} domain wall structures in the tetragonal phase of ferroelectric perovskites, one of the ``Ising type'' with only one polarization component and the other of the ``Bloch type'' with two polarization components within the wall layer, have been derived from the Landau-Ginzburg phenomenological theory. Temperature dependence of the interfacial energy indicates that the 180^∘{} wall has its own ``structural transformation,'' i.e., the wall structure is possible to change from Ising type to Bloch type upon cooling. As a more stable structure than the Ising-type wall in a wide temperature region, the Bloch-type wall has special crystal symmetry and physical properties which are presented in the report.